CR7.1

In recent years, subglacial hydrological models as well as till deformation models have been coupled to ice-flow models in order to determine mechanical basal conditions underneath ice sheets and glaciers. These models, nevertheless, often ignore the thermo-dynamical aspects, in particular, not including the influence of permafrost in proximity to or underneath glaciers. Here we present a thermo-mechanically coupled ice-sheet bedrock model. The latter includes components of saturated aquifer water transport, soil deformation, salinity transport and – most important – energy balance including phase change of the solvent. Using synthetic flow-line setups we present studies of ice-sheet fronts, advancing either over existing permafrost or largely unfrozen soils. We investigate the heat- and meltwater-transfer between the ice-body and its substrate and discuss their impact on ice-dynamics. As the results suggest that in certain situations the water balance further demands the existence of a hydrological system between ice and bedrock, we currently work to include this third model component in form of a subglacial hydrological model. All model components are implemented in the Finite Element software Elmer, which renders their mutual coupling relatively easy, yet, numerically demanding.

How to cite: Zwinger, T., Cohen, D., Gladstone, R., and Råback, P.: Modelling the thermal and mechanical interaction of an ice-sheet with a partly frozen bedrock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13099, https://doi.org/10.5194/egusphere-egu22-13099, 2022.

Coupled ice sheet - ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, and the wider implications of such processes. In particular, ice sheet - ocean interactions have a strong control on ice sheet stability and sea level contribution. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics, which, combined with the high cost of ocean models, can limit the timeframe that can be modelled. Here we present an "accelerated oceanic forcing'' approach to the ocean side of the coupling, in which the rates of change passed from ice model to ocean model components are increased by a constant factor and the period for which the  ocean model is run is correspondingly decreased. The ice sheet change over a coupling interval is thus compressed into  a shorter period over which the ocean model is run, based on the assumption that the ocean response time frame is shorter than  the compressed run period. We demonstrate the viability of this approach in an idealised setup based on the Marine Ice Sheet-Ocean Model Intercomparison Project, using the open-source Framework for Ice Sheet-Ocean Coupling (FISOC) combining two different ocean models (FVCOM and ROMS) and the ice-sheet model Elmer/Ice. We also demonstrate that the mean cavity residence time computed from the stand-alone ocean simulations can guide the selection of a suitable enhanced forcing factor for the coupled simulations. 

How to cite: Zhou, Q., Zhao, C., Gladstone, R., Hattermann, T., Gwyther, D., and Galton-Fenzi, B.: Accelerated oceanic forcing in coupled ice sheet-ocean modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10275, https://doi.org/10.5194/egusphere-egu22-10275, 2022.

Ice shelf melt rates near grounding lines are a few orders of magnitude higher than other locations. This intense melting close to
the grounding zone is crucial as it induces ice shelf thinning, further acceleration of ice flow, and grounded ice loss. However,
little is revealed about ice and ocean processes determining peak ice shelf melt rates close to the grounding line because (1) ocean
modelers apply a constant cavity geometry, (2) ice modelers typically assume some parameterizations for determining ice shelf melt rates,
and (3) ice-ocean coupled simulations typically require long model integration, necessitating coarse resolution, and they are not able to
resolve small-scale processes near grounding zones. Here, we develop an idealized high-resolution Pine-Island-like model configuration (250
m, 500m, and 1km horizontal and 10 m vertical grid spacings) and conduct ice-ocean coupled simulation for 20 years after 60 years of
initialization. We show that ice slope and ice shelf melt rate close to the grounding zone increases with higher grid resolution but ice
shelf geometry converges towards the highest resolution solution. We are also able to simulate the formation of sub-ice shelf channels by
applying seasonally varying oceanic conditions. We also present our preliminary results of ice-ocean coupled realistic Pine Island
simulation using unprecedentedly high horizontal and vertical resolution  (200m horizontal and 10 m vertical grid spacings). This is
a step towards understanding the ice-ocean interacting mechanisms determining ice shelf shape and melt rate, which is crucial for
improved projections of future Antarctic ice loss.

How to cite: Nakayama, Y., Hirata, T., and Goldberg, D.: What determines the ice shelf shape?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-80, https://doi.org/10.5194/egusphere-egu22-80, 2022.

How to cite: Naughten, K., De Rydt, J., Rosier, S., Jenkins, A., Holland, P., and Ridley, J.: Two-timescale response of the Filchner-Ronne Ice Shelf to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12129, https://doi.org/10.5194/egusphere-egu22-12129, 2022.

Glaciers in the Pacific sector of West Antarctica are losing mass at an accelerating rate. Superimposed on this long-term trend are interannual variations in mass balance that result from a combination of internal ice dynamics and variability in ocean-induced ice shelf melt rates. We explore the relative importance of these internal and external drivers of change, using a newly developed coupling between the 3D ocean model MITgcm, and the SSA ice flow model Úa. For present-day ocean conditions, we simulate persistent retreat of the Pine Island, Thwaites, Smith and Kohler grounding lines between 2020 and 2150. We demonstrate complex changes in ice shelf melt rates caused by the evolving cavity geometries.

How to cite: De Rydt, J. and Naughten, K.: Coupled ice-ocean modelling of the Amundsen Sea glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12248, https://doi.org/10.5194/egusphere-egu22-12248, 2022.

Increased warm water intrusions would cause mass loss in East Antarctica within 200 years

The East Antarctic Ice Sheet (EAIS) is the single largest potential contributor to future global mean sea level rise, containing 52.2 m of sea level equivalent. Current observations put the mass balance of the EAIS to be approximately stable (albeit with some margin of error), although future climatic conditions have the potential to change this. A warming climate is expected to have both a positive effect on ice sheet mass balance via increased precipitation and a negative effect via increased ice discharge over the grounding line, a process enhanced by ocean driven melting of floating ice reducing the buttressing effect of ice shelves. In addition to a general increase in the ocean temperature surrounding the EAIS there is the potential that future climatic shifts may increase the incidence of intrusions of warm Circumpolar Deep Water (CDW) onto the continental shelf, further increasing basal melting.

Here we show, by using a numerical ice-sheet model, simulations of the future EAIS under different  future climate scenarios, both with and without increased CDW intrusions. We find that without increased CDW intrusions the EAIS will have a negative contribution to sea level rise, with increased precipitation more than compensating increased ice discharge. If melting becomes predominately driven by CDW, however, our simulations find the EAIS to have a positive contribution to sea level rise. All simulations, both those with increased CDW forcing and those without, show an overall reduction in floating ice as well as a reduction in grounded ice area.

How to cite: Jordan, J., Gudmundsson, H., Jenkins, A., Miles, B., Stokes, C., and Jamieson, S.: Increased warm water intrusions would cause mass loss in East Antarctica within 200 years, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9710, https://doi.org/10.5194/egusphere-egu22-9710, 2022.

How well is the Antarctic climate over the last decades represented in climate models and how predictable is its future evolution? These questions delve into the specificities of the Antarctic climate, a system characterized by large natural fluctuations and complex interactions between the ice sheet, ocean, sea ice and atmosphere. The PARAMOUR project aims at improving our understanding of key processes which control the variability and predictability of the Antarctic climate at the decadal timescale. In this context, we introduce PARASO, a novel fully-coupled regional ocean - sea-ice - ice-sheet - atmosphere climate model over an Antarctic circumpolar domain covering the full Southern Ocean. The state-of-the-art models used are f.ETISh1.7 (ice sheet), NEMO3.6 (ocean), LIM3.6 (sea ice), COSMO5.0 (atmosphere) and CLM4.5 (land), which are run at a horizontal resolution close to 1/4°. One key feature of this tool resides in a novel two-way coupling interface for representing the ocean - ice-sheet interactions, through explicitly resolved ice-shelf cavities. We also consider the impact of atmospheric processes on the Antarctic ice sheet through surface mass exchanges between COSMO-CLM and f.ETISh. Our developments include a new surface tiling approach to combine open-ocean and sea-ice covered cells within COSMO. Using a 30 year-long run, we investigate the model performance and the interannual-to-decadal variability of the simulated Antarctic climate. The focus is on the interactions between the atmosphere, ocean and ice components at the regional scale and the links with larger spatial scales. Specific attention is paid to the mass balance of ice sheets and ice shelves, which influences both the ice sheet dynamics and the changes in the ocean and atmosphere. The system and its performance will be documented in this presentation together with some aspects of decadal variability from a 30-year integration forced with reanalyses (ERA5 and ORAS5). Early results of a 3-member retrospective forecast driven by EC-Earth will also be presented.

How to cite: Marchi, S., Pelletier, C., Fichefet, T., Goosse, H., Haubner, K., Helsen, S., Huot, P.-V., Kittel, C., Klein, F., van Lipzig, N. P. M., Massonnet, F., Mathiot, P., Moravveji, E., Moreno-Chamarro, E., Ortega, P., Pattyn, F., Souverijns, N., Van Achter, G., Vanden Broucke, S., Verfaillie, D., Le Clech, S., Vanhulle, A., and Zipf, L.: PARASO, a circum-Antarctic fully-coupled ice-sheet - ocean - sea-ice - atmosphere - land model involving f.ETISh1.7, NEMO3.6, LIM3.6, COSMO5.0 and CLM4.5, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4558, https://doi.org/10.5194/egusphere-egu22-4558, 2022.

Icebergs play a crucial role in Earth's climate system. They transport large amounts of fresh water and alter ocean salinity, affect sea-ice formation, and can lead to abrupt climate changes in the past. Hence, a proper representation of icebergs in Earth system models (ESMs) is essential to improve the understanding of processes involved in abrupt climate changes. Despite their importance, icebergs are rarely represented in ESMs. Freshwater fluxes are often parameterized, neglecting the transport via ocean currents and the heat loss due to iceberg melting. Other models that use an interactive iceberg component are typically ocean-only models, do not represent ice sheets and the atmospheric component explicitly, or are models of intermediate complexity. One reason for this deficiency is the considerable computational costs related to iceberg modeling.

Here, we present the latest version of the Alfred Wegener Institute-Earth System Model (AWI-ESM) with interactive ice sheets and a Lagrangian iceberg model. The iceberg component runs as a submodel of the ocean–sea-ice model FESOM2 with an asynchronous coupling to enable computationally effective simulations with the iceberg-enhanced coupled model. Total execution times can be strongly reduced compared to a non-overlapping execution of the iceberg model with other components. Iceberg meltwater and the associated heat fluxes are coupled to the ocean. The ice sheet is dynamically coupled to the climate components. A new feature of this model setup is the ice sheet-iceberg coupling: Icebergs are drawn from a specific size distribution to match the calving output of the ice sheet model in regions of iceberg discharge. Therefore, discharge-related freshwater fluxes are represented more realistically than in other ESMs.

How to cite: Ackermann, L., Rackow, T., Himstedt, K., Gierz, P., Knorr, G., and Lohmann, G.: A comprehensive Earth System Model (AWI-ESM) with interactive ice sheets and icebergs: A step towards realistic freshwater fluxes for abrupt climate change scenarios, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4608, https://doi.org/10.5194/egusphere-egu22-4608, 2022.

Icebergs calved from high-latitude glaciers and ice shelves pose a threat to vessels and offshore infrastructure at a time when Arctic shipping and offshore resource exploration are increasing. Knowledge of the location of potential ice hazards is therefore critical to ensure safe and efficient operations in this remote region. The Canadian Ice Service provides information to stakeholders on the observed and predicted distribution of icebergs in Canadian waters by combining iceberg observations with forecasts from the North American Ice Service (NAIS) iceberg drift model. The NAIS model estimates the forces acting on an iceberg to predict its future position and velocity and is widely used for the East Coast of Canada. However, the model is unproven for areas >60°N and suffers from insufficient validation due to a lack of reliable in-situ observations of iceberg drift. In this study, we use a newly compiled iceberg tracking beacon database to assess the skill of the NAIS iceberg model's predictions of iceberg drift and investigate sensitivity to morphology and environmental forcing (e.g., ocean currents, winds).

Hindcast simulations of the observed tracks of 44 icebergs over the period 2008-2019 were run using ocean currents from three ocean models (CECOM, GLORYS and RIOPS) and wind and wave inputs from the ERA5 reanalysis. Comparisons of several distance error metrics between observed and modelled drift tracks indicate that the NAIS model produces realistic simulations of iceberg drift in Baffin Bay. The root mean square error after the initial 24-hour hindcast period ranged from 18-22 km and increased at a daily rate of 11-13 km, which is comparable to operational forecasts elsewhere. Improved model performance was observed for longer (>250 m) and deeper-keeled (>100 m) icebergs, which appears to counteract the model’s tendency to overestimate drift by reducing the influence of stronger surface ocean currents acting on the iceberg. Ocean current direction, wind direction, and iceberg keel geometry were identified by a sensitivity analysis as the model parameters and environmental driving forces that have the greatest influence on modelled iceberg drift. These results emphasize the need for accurate environmental information and underscore the importance of properly representing the physical characteristics of icebergs in drift models.

How to cite: Garbo, A., Copland, L., Mueller, D., Tivy, A., and Lamontagne, P.: Validation of the North American Ice Service iceberg drift model using a novel database of in-situ iceberg drift observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10657, https://doi.org/10.5194/egusphere-egu22-10657, 2022.